1. Field of the Invention
This invention relates to a thermosettable composition including an amphiphilic block copolymer, a polyol, an anhydride, an epoxide and a catalyst; and thermoset products made from such thermosettable composition. The thermoset products made from the thermosettable compositions of the present invention have improved mechanical performances, especially toughness and mechanical strength, thermosettable compositions, while maintaining high thermal resistance. The compositions of the present invention are useful in various applications such as casting, potting, and encapsulation, such as electrical and electronics applications, and composites.
2. Description of Background and Related Art
Some thermosetting resins are known to have good toughness and good mechanical properties, some thermosetting resins are known to have good thermal resistance, and some thermosetting resins are known to have good processability. However, heretofore, a thermosetting resin exhibiting each and every one of the above characteristics to the extent that such thermosetting resin can be prepared in large scale, and used in high performance applications under significant stress and moisture exposure, has not been made.
There is a need for thermosetting resins with improved mechanical properties (e.g. higher toughness and mechanical strength) while maintaining good thermal resistance and good processability of the resin. High toughness and high mechanical strength leads to less cracking and high mechanical integrity, reducing the number of defects and improving the reliability and life time of the end products. High thermal resistance enables high operation temperature. Low formulation viscosity improves processability and enables high filler loading.
Heretofore, those skilled in the art have attempted to improve the properties of thermosetting resins by adding various additives, such as flexibilizers and toughening agents, to the thermosetting resin. However, the use of conventional flexibilizers such as linear polyols in thermosetting resin only leads to a moderate improvement in toughness; and significantly reduces the thermal stability of the thermoset because of the resulting low (less than 100° C.) glass transition temperature. The use of conventional toughening agents in the thermosetting resin leads to processing issues because of the high viscosity of the resulting formulation, and because of the complexity of the phase-separation process.
For example, the use of conventional toughening agents such as liquid rubbers, core-shell particles and thermoplastic polymers, in thermosetting resins increases the toughness of the thermosetting resin at the cost of adversely affecting some other properties of the thermosetting resin such as glass transition temperature, mechanical properties, viscosity, etc. It is difficult to maintain the glass transition temperature and mechanical strength when liquid rubbers and thermoplastic polymers are employed to improve toughness; and due to the nature of core-shell particles, it is hard to fully disperse these particles into a thermosetting resin such as an epoxy resin without additional treatments.
Still, there are various prior art technologies that have been used to attempt to toughened thermosetting compositions. For example, EP126494A1 describes a composition which contains a specific group of hardeners, an epoxy resin and a thermo-plastic polymer. When combined with a structural fiber the composition produces composites which have improved impact resistance, improved tensile properties and high compressive properties. However, EP126494A1 describes a conventional toughening method by adding a thermoplastic polymer into a thermoset; and discloses the incorporation of a thermoplastic polymer into an epoxy resin system to improve its impact resistance. EP126494A1 uses a thermoplastic polymer toughening agent; it does not teach employing an amphiphilic block copolymer as the toughening agent in the epoxy resin system.
U.S. Pat. No. 4,497,945 discloses forming a tough epoxy polymer by pre-reacting a poly(oxypropylene)diol or triol with a chemical excess of an anhydride curing agent for epoxy resins. The resulting diester-diacid is then polymerized with an epichlorohydrin-bisphenol A epoxy resin. Suitable imidizole catalysts are preferred for the reactions. However, U.S. Pat. No. 4,497,945 does not disclose the use of a toughening agent; and does not teach the use of an amphiphilic block copolymer as the toughening agent in an epoxy resin system.
U.S. Pat. No. 4,551,520 discloses that polyesters of 95 to 40 mol % terephthalic acid, 5 to 60 mol % trans-4,4′-stilbenedicarboxylic acid, and at least 60 mol % 1,4-cyclohexanedimethanol can be injection molded to give shaped objects having exceptionally high impact strength and good chemical resistance. In addition, the polyesters of U.S. Pat. No. 4,551,520 can be extruded into films, spun into fibers, or blown into bottles having these properties. U.S. Pat. No. 4,551,520 does not use a toughening agent; and does not teach the use of an amphiphilic block copolymer as the toughening agent in an epoxy resin system.
U.S. Pat. No. 4,846,905 discloses a thermally-curable, one-part epoxy adhesive composition comprising: (1) a glycidyl ether epoxide having an epoxy functionality greater than one and a molecular weight between about 150 and 10,000; (2) a catalyst comprising (i) an acid of the formula H+SbF5X—, wherein X is halogen, hydroxy, or —OR, and wherein —OR is the residue of an aliphatic or aromatic alcohol having a molecular weight less than about 10,000 and (ii) N,N-diethyl-o-toluidine; (3) an aliphatic or non-aromatic cyclic polyol having about 2 to 18 carbon atoms, at least two hydroxyl groups of which are primary or secondary, and being free of electron-withdrawing substituents, amine substituents, or large substituents that cause steric hindrance in the α-position in relation to the carbon attached to the methylol group of the polyol; and (4) a toughening agent that does not react with the epoxide during curing and has an epoxide compatible component and an epoxide incompatible component.
U.S. Pat. No. 4,846,905 discloses an epoxy resin composition comprising a polyol and a toughening agent. However, U.S. Pat. No. 4,846,905 describes different toughening agents; and the toughening agents can be divided into three types:
1. A polymerized, diene, rubbery backbone or core to which is grafted a shell of an acrylic acid ester or methacrylic acid ester, monovinyl aromatic hydrocarbon, or a mixture thereof.
2. A core-shell graft copolymer wherein the core or backbone is a polyacrylate polymer having a glass transition temperature below about 0° C.
3. Elastomeric particles having a glass transition temperature below about 25° C., and have been polymerized in situ in the epoxide before mixing with the other component of the composition.
All the above three types of toughening agents (core-shell particles and elastomeric particles) differ from an amphiphilic block copolymer toughening agent. None of the prior art technology utilizes a reactive toughening agent which reacts with an anhydride and possibly with an epoxy.
U.S. Pat. No. 5,382,628 discloses thermoformed plastic articles such as frozen food trays, which exhibit unexpectedly high impact strength at low temperatures. The articles are obtained from polyester blends containing 88 to 99 weight percent of a poly(ethylene terephthalate) resin and 1 to 12 weight percent of a poly(1,4-cyclohexylenedimethylene terephthalate) resin which contains at least 30 mole percent of 1,4-cyclohexanedimethanol.
U.S. Pat. No. 5,382,628 describes thermoplastic PET materials thermoformed into plastic articles. U.S. Pat. No. 5,382,628 does not disclose the use of a thermoset formulation comprising an amphiphilic block copolymer as the toughening agent in an epoxy resin system.
WO1998001495A1 discloses epoxy resin systems having good flexibility and impact resistance that are modified to provide improved resistance to solvents. Incorporation of a polyalkyleneoxide segment of a molecular weight less than 500 provides improved chemical resistance without sacrifice of mechanical properties. To achieve this, an alkoxylated polyol with low molecular weight is reacted with a polycarboxylic acid anhydride to produce the half ester, which is then used to synthesize the flexibilized epoxy resin by forming adducts with polyglycidyl ethers. The flexibilized epoxy resins as well as the acid functionalized oligooxyalkylenes are taught in WO1998001495A1.
However, the technology in WO1998001495A1 uses a polyol modified hardener to flexibilize the network, but does not use a toughening agent. WO1998001495A1 does not teach the use of an amphiphilic block copolymer as the toughening agent in an epoxy resin system, which affords improved flexibilization and maintains Tg.
U.S. Pat. No. 5,789,482 discloses epoxy resin compositions which contain (a) at least one epoxy resin containing, on average, more than one 1,2-epoxy group per molecule, (b) an anhydride hardener for the epoxy resin (a), (c) a toughener, and (d) a compound containing two active hydrogen atoms which is capable of reacting with the epoxy resin (a) have an outstanding toughness and are suitable as casting resins, laminating resins, moulding compounds, coating compounds and encapsulation systems for electrical and electronic components.
U.S. Pat. No. 5,789,482 teaches that a core/shell polymer toughener is incorporated into the system to improve the toughness, which is different from incorporating an amphiphilic block copolymer as the toughening agent. Also, U.S. Pat. No. 5,789,482 does not contain a hydroxycarboxylic acid, a dicarboxylic acid, or a biphenol, which is a mononuclear diphenol, dihydroxy naphthaline, dihydroxy biphenyl or another binuclear aromatic compound which has a methylene, isopropylidene, O, SO2 or S bridge and contains two hydroxyl groups bound to the aromatic nuclei and wherein the benzene rings may also contain halogen atoms.
WO2006052729A1 discloses a curable epoxy resin composition including (a) a thermosettable epoxy resin; and (b) an amphiphilic block copolymer containing at least one epoxy resin miscible block segment and at least one epoxy resin immiscible block segment; wherein the immiscible block segment comprises at least one polyether structure provided that the polyether structure of said immiscible block segment contains at least one or more alkylene oxide monomer units having at least four carbon atoms, such that when the epoxy resin composition is cured, the toughness of the resulting cured epoxy resin composition is increased. The amphiphilic block copolymer is preferably an all polyether block copolymer such as a PEO-PBO diblock copolymer or a PEO-PBO-PEO triblock copolymer.
WO2006052729A1 describes the use of amphiphilic toughening agents in epoxy resin formulations. However, the technology described in WO2006052729A1 does not teach or suggest an improvement in: (i) the flexural modulus; (ii) the tensile strength, tensile elongation, KIc, and flexural strain; or (iii) the Tg values.
Thus, there is still a need in the industry for thermosetting resins which show an improvement in its mechanical properties such as tensile strength and flexural strength, while increasing toughness and without significant reduction of thermal stability as defined by the glass transition temperature, especially when compared with conventional toughening technologies.
It therefore desired to provide thermoset products with improvements to one or more of the above properties and characteristics over conventional thermosets.